U.S. Attorney General Eric Holder pauses while testifying before the House Judiciary Committee on Capitol Hill in Washington earlier this month. The government is now saying that a Fox News reporter committed a crime for disclosing information leaked to him by a Whitehouse advisor.

WASHINGTON — In another case of the Obama administration investigating classified information improperly disclosed to reporters, the government is prosecuting a State Department expert on North Korea in a probe that appears to step into uncharted territory — by declaring that a journalist is committing a crime in disclosing leaked information.

During the investigation of State Department adviser Stephen Kim, law enforcement officials obtained a search warrant for some private emails of James Rosen, the chief Washington correspondent for Fox News. Investigators also tracked Rosen’s comings and goings from the State Department.

An FBI agent seeking the search warrant spelled out the government’s view of the journalist’s role, saying the reporter is a co-conspirator and that there is probable cause to believe that the reporter committed a violation of criminal law.

“We are outraged to learn today that James Rosen was named a criminal co-conspirator for simply doing his job as a reporter,” said Michael Clemente, Fox’s executive vice president for news. “In fact, it is downright chilling. We will unequivocally defend his right to operate as a member of what up until now has always been a free press.”

Kim, who is awaiting trial, is accused of revealing secrets to the news organization. No charges have been filed against Rosen.

The Kim case is further along than a more recent leak probe in which prosecutors secretly subpoenaed Associated Press phone records. In the AP case, AP President and Chief Executive Gary Pruitt said the government’s conduct has already had a chilling effect on newsgathering, a week after the AP subpoenas were revealed publicly.

In June 2009, Rosen reported that U.S. intelligence officials warned President Barack Obama and senior U.S. officials that North Korea would respond to a United Nations Security Council resolution condemning nuclear tests with another nuclear test.

The 2010 affidavit for a search warrant, first reported by The Washington Post, does not identify Rosen as “the reporter,” but he wrote the story at issue, and Fox News confirmed it was him on Monday.

The White House wouldn’t comment about tracking Rosen, citing an ongoing criminal investigation. Instead, White House spokesman Jay Carney cited a media shield law Obama supports as evidence of his commitment to journalistic freedom, reprising an argument the White House used a week earlier in declining to address the Justice Department’s probe involving AP.

“The president believes it’s important that we find a proper balance between a need — absolute need — to protect our secrets and to prevent leaks that can jeopardize the lives of Americans and can jeopardize our national security interests on the one hand, and the need to defend the First Amendment and protect the ability of reporters to pursue investigative journalism,” Carney said.

In the Kim case, “based on the investigation and all of the facts known to date, no other individuals, including the reporter, have been charged since Mr. Kim was indicted nearly three years ago,” said the U.S. Attorney’s office in Washington, D.C., which is prosecuting the case.

The Justice Department said that improper disclosure of classified information to the press can pose a serious risk of harm to national security, and said it has followed the law and its policies to protect First Amendment rights.

The material at issue in the Kim case came from an intelligence report that had been communicated to officials in the intelligence community, including Kim, on the morning that Rosen’s story was published, according to the affidavit for a search warrant by FBI agent Reginald Reyes. Between the time of that communication and when the story was published, someone with Kim’s unique electronic profile and password accessed the report at least three times.

Citing telephone call records, the affidavit also said that multiple phone calls were made between the two that day, including two from Kim when someone with his profile was viewing the report. The FBI agent also cited multiple calls between Kim’s cellphone and Rosen and his news organization.

The FBI went well beyond phone records to try to establish a connection between the two. The agent wrote that State Department security badge access records showed that Kim and Rosen, who had an office at the State Department at the time, left the building at nearly the same time that day, were gone for about 25 minutes, and returned around the same time. The FBI affidavit also said that when State Department Diplomatic Security personnel entered Kim’s office space two months later, they found Rosen’s article “lying in plain view” on Kim’s desk.

The affidavit stated that the email communications, obtained by search warrants on Kim’s Yahoo email accounts, show Rosen and Kim used aliases — “Alex” and “Leo,” respectively. In one email, Rosen writes: “What I am interested in, as you might expect, is breaking news ahead of my competitors ... Let’s break some news, and expose muddle-headed policy when we see it.”

Rosen encouraged Kim to disclose sensitive U.S. internal documents and intelligence about North Korea (identified only as the “Foreign Country”), according to the affidavit.

“The reporter did not possess a security clearance and was not entitled to receive the information published in the June 2009 article,” wrote Reyes, the FBI agent.